1. Field of the Invention
The present invention relates to noise reduction in computer systems and more particularly, to enclosures for reducing the level of noise emitted by a computer component such as a hard disk drive or other data storage disk drive device.
2. Background of the Invention
As personal computers have proliferated in the work place and home, concern has increased about their effect on the work and home environments. One subject of concern is the effect of noise generated while the computer is in operation. The fans, the disk drives, and the power supply all produce noise during operation. Hard disk drives, in particular, operate at relatively high rotation speeds and produce most of this noise. In addition, current disk drive designs use higher spindle speeds and head actuator speeds to provide faster access times. Such improvements, while enhancing storage capacities and reducing data access times, have resulted in increased acoustic noise. This noise unnecessarily pollutes the office environment. Noise has been associated with increased levels of stress and other physiological effects.
Attempts to reduce acoustic noise generated by hard disk drives have generally followed one of two approaches. An example of the first approach is described in U.S. Pat. No. 5,282,100, issued to Tacklind et al. In the disclosed system a generally flat, box-shaped hard disk drive module has two exterior major surfaces which are acoustically decoupled from the noise generating components of the disk drive device by resilient gaskets. This arrangement somewhat reduces propagation of acoustic noise generated within the module when combined with an insulating film applied to the enclosure surfaces. However, conventional resilient materials for gaskets do not sufficiently attenuate vibrations to provide the full acoustic decoupling needed for a highly effective sound-reducing enclosure.
The second approach uses a sound absorbing material surrounding the drive module to insulate the external environment from the noise generated by the disk drive device. An example of this arrangement appears in U.S. Pat. No. 5,510,954, issued to Wyler. A sound absorbing layer surrounds the disk drive module, and an air-tight enclosure may further surround the sound absorbing layer. This approach utilizes the high sound attenuation properties of various modern insulating materials effectively to prevent disk drive noise from propagating away from the enclosure.
The Wyler device recognizes a substantial problem that arises from enclosing the disk drive in an insulating material, which is that sound insulating materials generally provide heat insulation as well. Heat retention within the disk drive module risks producing a worse problem than noise, because elevated operating temperatures can cause the performance of a disk drive to degrade seriously. To solve this problem, the Wyler device includes a heat sink on an exterior face of the enclosure and a heat conductive path from the heat sink through the sound absorbing layer to the disk drive device. The proximal end of the heat path connects to a metal bracket that partially surrounds the drive module and thereby acts as both an additional layer of sound insulation and as a cold plate.
The Wyler arrangement effectively reduces the noise emitted from the disk drive enclosure, but it also has several limitations. First, the heat sink must be separately mounted externally relative to the sound absorbing layer. Also, the device works best when the heat conducting path consists of copper braiding or another metal with relatively high thermal conductivity. This requirement arises from the fact that the heat conducting path joins both the heat sink and the "cold plate" metal bracket, respectively, in relatively small areas. Sufficiently rapid heat transfer therefore requires that the heat conducting path consist of a conductivity-optimized material, such as pure copper.
For greatest effectiveness, the heat conducting path must also join the heat sink and the metal bracket with metal-to-metal contact, such as by bolting or soldering. The joints therefore require separate attachment operations during manufacture of the device, and these operations must comply with high quality control standards to ensure that a faulty heat channel does not cause the disk drive to overheat. Such requirements do not diminish the value of the device once fabricated, but they do increase the cost of fabrication. Manufacture of the Wyler enclosure may also be complicated by its modular construction from discrete insulating panels, which increases the costs of assembly even further.
Another serious limitation of the Wyler device arises from the fact that it structurally isolates the disk drive module from system chassis to which the enclosure is attached. The module has no positive attachment to the chassis, but instead is supported on all sides by resilient insulating material. Such isolation enhances the enclosure's noise-confining performance, but it does so at the risk of allowing the drive module to become mobile within the insulating layer. If any part of the layer becomes compressed, due to forces from the module itself in response to shocks, for example, then the module will freely float in a cavity. The cavity will likely enlarge rapidly as the module progressively develops more and more momentum in response to shocks to the enclosure. The reliable lifespan of the enclosure is therefore uncertain at best, and the first indication of its failure will likely be a catastrophic failure of the disk drive device.
I have noticed, therefore, that a continuing and unmet need exists for a noise reducing disk drive enclosure that effectively combines the advantages of acoustically decoupled systems and sound absorption systems. Such an enclosure should provide both the positive structural support of acoustically decoupled systems and the effective noise attenuation of sound absorption systems. It should also address the heat build-up problem inherent in the use of insulating materials. Preferably, such a system would conform to existing disk drive configurations. Ideally, it would utilize conventional materials available at low cost and could be implemented with simple manufacturing operations.